1. Field of the Invention
The invention relates to a shipping crate formed from sheets of corrugated material, such as paper board, and in particular to a crate whose design optimizes compression strength relative to the amount of material that is use to make the crate.
2. Brief Description of the Prior Art
Shipping crates made from corrugated board are gaining popularity over wooden crates due to weight benefits as well as concerns of insects being carried in the wood. The crates are manufactured so that the flutes of the corrugated board are vertical, because it is well known that the vertically orientation can support far more weight than horizontally oriented fluting. The compression strength, or load bearing strength, of corrugated board crates is then strengthened by adding additional corrugate layers and/or by increasing the weight of the corrugated board that is used.
The need for high load bearing strength is based on the fact that crates are frequently stacked in storage and during shipment. Crates may be stacked two or three high, and instances they can be stacked four high. The bottom crate must support the weight of all of the crates above it.
A cargo carrier is typically a metal shipping container and shipping crates are generally manufactured to have dimensions such as that, in combination, they will substantially fill the 8×8×40 ft. interior space the cargo carriers. The crates can be any combination of sizes that readily combine to fill the 8×8×40 foot interior. In those instances where the interior space of the cargo transporter is other than a standard 8×8×40 feet, then the crate can be dimensioned to correspond to the interior dimension of the cargo transporter. Long distance shipping crates, and particularly crates for international shipping of goods, are predominantly designed to provide, approximately, an eight foot, by eight foot, by four foot interior space.
The container capacity is the total cubic volume (cube) a container can accommodate, or the cubic measurement of cargo. The capacity (i.e., the internal volume) is determined by multiplying the internal dimensions, that is, the product of internal length, width and height. The capacity may vary among containers of the same specified length and height.
The use of two or three layers of corrugated paper significantly increasing the crush strength. As the cost of the crate is directly related to the amount of corrugated paper that is used. the material cost of a double wall 1,300 pound paper would about two thirds the cost of a 1,300 pound triple wall corrugated paper.
A double wall corrugated has two outer layers of flat sheet material, two layers of fluted sheets and a third layer of flat sheet material between the two fluted layers. A triple wall panel has two outer layers of flat sheet material, three layers of fluted sheets and two layers of flat sheet material separating the three fluted layers. A triple wall panel thus has a flat sheet, fluted sheet, flat sheet, fluted sheet, flat sheet, in that order. As the flat sheets use less material per running foot than a fluted sheet, the triple wall has very nearly one third more material than a double wall, which is reflected in the cost. The weight of the corrugated material will also be reflected in the price. Corrugated sheet that are classified as 1,000 weight would cost double that of 500 weight corrugated.
The compression resistance of crates can be tested by using r ASTM D4169/D642. Failure of crates tested under ASTM D4169/D642, occurs when the crate compresses to any extent. The tests are all run to failure and since the tests are run in twenty pounds increments, the compression prior to failure, that is, the maximum compression strength, is twenty pounds less than compression at failure.